1. Field of the Invention
The present invention relates to a semiconductor device, and in particular to a semiconductor device mounted with a fuse.
2. Description of the Related Art
Mounting of a fuse on a semiconductor device makes it possible to adjust value of resistors used in the semiconductor device or replace a defective element with a normal element, by once disconnecting the fuse. This technique of replacing a defective element with a normal element is typically applied to redundancy design of the semiconductor memory device. Disconnection of the fuse is often achieved by blowing it off with a laser. The method of blowing the fuse off using the laser, however, raises several problems.
A first problem resides in that a position of disconnection of the fuse must be apart from other elements by a predetermined distance so as to avoid any possible influences of the laser-assisted disconnection of the fuse, and this increases the device size in view of securing a sufficient space therefor.
The next problem is that one or two dedicated lithographic process steps are further required to form the fuse in addition to the general process steps, and this consequently results in larger cost and longer process time. More specifically, the fuse will generally have an interlayer film formed thereon, so that it is necessary, in the final process step, to form an opening for the convenience of laser irradiation in the interlayer film so as to adjust the thickness of the interlayer film on the fuse. In evaluation of any products incorporated with the fuse, it is essential to carry out a series of process steps of “characteristic inspection”, “disconnection of fuse by laser irradiation” and “characteristic re-inspection”. This undesirably results in further elongation of the process steps and increase in the cost.
To solve the above-described problems in the laser-assisted disconnection of the fuse, a proposal is made on current-assisted meltdown of the fuse in place of using the laser. As one typical method of facilitating the current-assisted disconnection of the fuse, Japanese Laid-Open Patent Publication No. 2000-40790 discloses a procedure of narrowing as possible a meltdown portion of the fuse by oblique ion implantation through a mask formed on the meltdown portion of the fuse.
The fuse disclosed in Japanese Laid-Open Patent Publication No. 2000-40790 can certainly reduce current and/or voltage necessary for meltdown the fuse, but further reduction in the current and/or voltage for meltdown will be necessary if the semiconductor devices mounted with the fuse are desired to be applied to circuits driven under low voltage, in consideration of influences on other elements.